Photomultiplier tubes (PMTs) are used to detect light that comes from gamma-ray-initiated showers in the earth's atmosphere. The gains of the PMTs are key to determining the amount of light detected and, subsequently, the energy of the incoming gamma ray. In this thesis, a new method of measuring the gain of a PMT is proposed. It relates the PMT gain to the variance of the PMT signal divided by the average current. The new method is mathematically motivated, tested with a series of experiments, and verified using simulations. In addition, it is compared with an existing method of measuring the gain. The new method is shown to be able to predict the gain to within a constant of multiplication. This constant is intrinsic to each PMT and varies from one PMT to another.

The design of a system for studying human eyeball movements is presented. The system output provides eyeball location and pupil size in the form of step-wise voltages which are up-dated a minimum of 4000 times per second. Eye movements up to ± 45 degrees in two dimensions can be tracked. The frequency response of the system ensures continuous tracking of all eye movements including the fastest saccades. The method employed is a photoelectric scan which uses feedback to lock onto the pupil and follow its movements. In the final system, this is performed by a scanning photo-multiplier tube which electronically dissects an optical image of the eye. To check the feasibility of the proposed system before the scanning photomultiplier is purchased, the work is performed in two parts: first the circuitry required to perform the scan is developed and tested without the use of a scanning photomultiplier tube; then an experiment is performed which simulates the scanning photomultiplier and enables the over-all system performance to be evaluated. In the first part, a system is constructed which performs similarly to the final system except that the electronic dissection of the image is performed using an oscilloscope in conjunction with a simple photomultiplier instead of the scanning photomultiplier. This "flying-spot system" is used to test the circuitry required to perform the scan: the circuitry proves to be entirely, satisfactory. In the second part, the simulation enables the signal noise ratio of the scanning photomultiplier to be predicted. On the basis of this, a recommendation is made to purchase the scanning photomultiplier and to construct the complete system. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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Thesis (Ph. D.)--University of Iowa, 2003. / Supervisor: Yasar Onel. Includes bibliographical references (leaves 154-164).

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A maximum-likelihood parameter-estimation method is developed that allows the mean of coarsely digitized data to be determined to far greater precision than that inherent in the digital quantization. The method is used to determine the mean responses of photomultiplier tubes in a medical scintillation camera. The mean responses as determined by the estimation scheme are applied to two tasks. The first is the development and construction of a feedback-control loop to stabilize photomultiplier tube responses. The second is a method to characterize the camera face for the construction of a look-up table of maximum a posteriori position estimates used in image acquisition. The implementation of the parameter-estimation algorithm, its applications in both the stabilization of photomultiplier tube response and image look-up table construction, and the analysis of photomultiplier tube statistics, are considered to be the major contributions of the work presented in this thesis. (Abstract shortened with permission of author.)

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Electron orbital theory was applied to the design of the geometrical structure of an electron multiplier for an image intensifier. A special structure satisfying production requirements was studied. Electron optical calculations consisted of determining the potential distribution and tracing the electron trajectories. Liebmann’s procedure was used to solve Laplace’s equation with constant potentials on the multiplier electrodes as boundary conditions. The trajectories were determined by solving the equation of motion in an electrostatic field using a Runge-Kutta procedure. The initial conditions for the trajectories were the initial energies, initial positions, and the initial directions of the secondary electrons. The plotted trajectories indicated the feasibility of an electron multiplier of the type studied.

Current state-of-the-art environmental, clinical, and in-vivo radiation sensing systems utilizing various inorganic and tissue-equivalent plastic scintillators are not user friendly, suffer from electron-beam-generated noise, and are difficult to deploy successfully for real-time dosimetry. A robust, real-time detection system using different scintillating materials coupled to solid-state detectors by optical fibers is developed. This system enables radiation monitors/clinicians to conduct meaningful real-time measurements using different inorganic scintillators or organic, tissue-equivalent plastic scintillators in harsh clinical and environmental environments. Recent solid state photomultiplier (SSPM) technology has matured, reaching a performance level that is suitable for replacement of the ubiquitous photomultiplier tube in selected applications for environmental radiation monitoring, clinical dosimetry, and medical imaging purposes. The objective of this work is laboratory and clinical testing of the Hamamatsu MPPC (S10362-11-050C), Photonique SSPM (0810G1), and Voxtel SiPM (SQBF-EKAA/SQBF-EIOA) SSPMs coupled to different inorganic scintillator crystals (Prelude 420, BGO), inorganic doped glass scintillator material SiO₂: Cu²⁺, and organic BCF-12 plastic scintillating fibers, used as detector elements. Both polymer optical fibers (POFs) and glass optical fibers (GOFs) are used as signal conduits for laboratory and clinical testing. Further, reduction of electron-beam-generated Cerenkov light in optical fibers is facilitated by the inclusion of metalized air-core capillary tubing between the BCF-12 plastic scintillating fiber and the POF. Dose linearity, percent depth dose, and angular measurements for 6 MV/18 MV photon beams and 9 MeV electron beams are compared using the Hamamatsu MPPC with-and without the use of the metalized air-core capillary tubing for BCF-12 plastic scintillating fiber. These same measurements are repeated for SiO₂: Cu²⁺ scintillator material without air-core capillary tubing. / Graduation date: 2012